Muscle strength: Muscle strength of hip extensors, -flexors, knee flexors and -extensors, and ankle flexors and extensors, in addition to ankle plantar flexion will be tested isokinetically according to the manufacturer's manual (Cybex 6000). Isokinetic muscle testing is commonly used in the literature in various patient populations (Inkster et al. 2003; Holm et al. 2000b; Brox et al. 1995; Lephart et al. 1993; Newton et al. 1993). The test protocol will consist of five repetitions at an angular velocity of 60 deg/sec at maximal performance. In order to prepare patients for the test, eliminate learning effects and to obtain stable performance, patients will be given four test-repetitions at the same speed before the main test. An experienced physical therapist will perform the test.